ML20077R682

Paper Entitled, State Point Experiments for Tight Lattice of 4.81 W/O Enriched UO2 Fuel Pins, to Be Presented at ANS Meeting in San Francisco,Ca

ML20077R682
Person / Time
Site:	Rensselaer Polytechnic Institute
Issue date:	08/08/1991
From:	Harris D, Hayes D, Rohr R RENSSELAER POLYTECHNIC INSTITUTE, TROY, NY
To:
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ML20077R679	List: ML20077R677 ML20077R682
References
NUDOCS 9108230275
Download: ML20077R682 (4)

Text

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i State Point Experiments for a Tight Lattice of 4.81 w/o Enriched UOa Fuel Pins f

l D. R. Harris, R. C. Rohr, and D. K. Hayes I

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Rennselaer Polytechnic Institute l

Troy, New York l

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t Reactor critical experiments have as their principal objective the j i

guidance of improvements in reactor physics calculations. Hence these l I

experiments should be designed and reported so as to best facilitate this i t

objective. To do this it is necessary to take into account the-casic .I

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. features both of the calculations and the experiments. Here we recommand {

the state point method for design and reporting-of fuel pin type criticals, and we illustrate by new results for a tight lattice of 4.81 w/o enriched UO2 fuel pins (1). These results were measured recently at the RPI Reactor Critical Facility _ (RCF), which is currently the only facility in North America providing critical experiment data in suppert-of the light water reactor electric power industry. 'The reported-upon

'SPERT lattice (0.58S in, pitch) has now been removed and replaced by an ,

t ABBCE lattice, and this is to be followed in 1992 by a O.613: in. pitch SPERT latticw. The RCF has a new boric acid capability, and results with boric acid in the water are reported on here for the first time. .

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A. state point is def.ined here as a1 fixed reactor configuration, a fixed j

'and-uniform set-of thermodynamic parameters, all control rods fully-- j r

withdrawn. and' core. fully submerged. A' state point is described by the j i

specification of reactor configuration. the measured thermodynamic parameters, the measured reactivity. and the measured power shape.  :

~Figura 1 snows measured state points for a series'of fuel pan configurations. both with and without beric acid. At higher temperatures

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less boric acid and/or more peripheral fuel pins are required to maintain

. the oesired supercriticality. The state point method in to be contrasted a

with methods in which criticality is maintained by adjusting control rods or water height. State points as here defined can be calculated-dire-tly l and unamDiguously by reactor physica design methods, noting that axial leakage is usually treated via the measured axial buckling. Reactor physics methods have_ difficulties with the complicated axial reflectors.

ad hoc control rods, and spectral mismatch at the water surface used at various critical facilities. Each of the state points in Figure 1 can be ,

calculated directly and unambiguously by reactor physics design methodn.

Moreover, the measured state points can be subjected to reproducibility tests (for examplet reboration, fuel pin exchange, repeated control red  ;

scrams). For the reported core it han been found that reproducibility is ,

within 1/2 cent, and the standard error of each reactivity point is about  !

1/4 cent. exclusive of errors in delayed neutron data. l

' The temperature coefficient of reactivity, alpha. is found directly from the data in Figure 1. and results are shown in Figure a for the cano ef no boric acid. Also shown are calculated values and values measured I 1

against control red height (dg/dT=d /dt*d:/dT). The latter method assumes that alpha is independent of control rod height. an assumption which is very difficult to confirm from calculations or measurements.

The inference of alpha from state point data can be confirmed easily from.

calculations. because it is found that alpha is essenttally independent

of fuel rod number. .

Pef or enc e

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1. - D . R. Harris. R. C. Rohr, P. L. Angelo. N. T. Patrou. K. W.-Duckwheat.

D. K. Hayes. "Meaturements of Fuel Pin / Water Hole Worths and Power i

Peaking. Void Coefficients. and Temperature Coefficients for 4.81 w/o l Enrichec UO2 Fuel Rods". Trans. Am. Nucl. Soc. gg, 576(1990). l i

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27 + 1 ppm Boron as Doric Acid 1

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l 3 g 50 70 90 110 130 Temperature (F)

Figure 1. Measured State Points for Lattices of 4.81 v/o U235  ;

UO2 Fuel Pins with Indicated Number of Fuel Pins

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McTsured from State Points

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~1* i i , , i e i 50 70 90 110 13'O Temperature (F) l Figure 2. Torporature Coef ficient Alpha (c/F) Versus Reactor Temperaturo (F) l l

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